Aircraft instrumentation enables pilots to fly aircraft under conditions of poor visibility. In view of the importance of instruments, devices have been developed for simulating flight conditions of poor or no visibility in order to train a pilot in instrument landing and flight procedures. However, instruments can fail and it is important for a pilot to be able to fly safely insofar as possible upon instrument failure. Therefore, practice under conditions of simulated instrument failure is an important part of flight training. The various instruments have different susceptibilities to failure, and it is not unusual for only one of a group of instruments to fail at one time. It would therefore be desirable to be able to simulate a realistic situation involving failure of one or more instruments during flight training and to do it safely.